Patent Document 1 shows a publicly known switching power supply circuit which is a switching regulator of peak detection topology; can utilize a low ESR capacitor, such as a ceramic capacitor, for load capacity; is capable of stable operation even at an oscillation frequency of several MHz or more and also provides high stability under load; and can reduce a layout area.
The switching power supply circuit disclosed in Patent Document 1, however, is dedicated to step-down conversion, thus posing the problem that it is not usable under conditions where an input voltage is higher or lower than an output voltage.
On the other hand, there is a buck-boost switching power supply circuit which can utilize a low ESR capacitor, such as a ceramic capacitor, for load capacity; and is capable of stable operation even at an oscillation frequency of several MHz or higher. Such a switching power supply circuit has been made known to the public by Patent Document 2.
The switching power supply circuit according to Patent Document 2 is of a so-called current mode control type which detects a coil current and controls a switching action based thereon. This type of switching power supply circuit requires the detection of the coil current.
With conventional technologies including that of Patent Document 2, when a coil current is to be detected, a technology using a coil current sensing circuit has been in wide use. This technology is adapted, for example, to insert a sense resistor in series with a coil, amplify the values at both ends of the sense resistor with a current amplifier, and connect the output of the current amplifier to the output of an error amplifier via a coupling capacitor.